25th Anniversary Article: Scalable Multiscale Patterned Structures Inspired by Nature: the Role of Hierarchy

Abstract

Multiscale, hierarchically patterned surfaces, such as lotus leaves, butterfly wings, adhesion pads of gecko lizards are abundantly found in nature, where microstructures are usually used to strengthen the mechanical stability while nanostructures offer the main functionality, i.e., wettability, structural color, or dry adhesion. To emulate such hierarchical structures in nature, multiscale, multilevel patterning has been extensively utilized for the last few decades towards various applications ranging from wetting control, structural colors, to tissue scaffolds. In this review, we highlight recent advances in scalable multiscale patterning to bring about improved functions that can even surpass those found in nature, with particular focus on the analogy between natural and synthetic architectures in terms of the role of different length scales. This review is organized into four sections. First, the role and importance of multiscale, hierarchical structures is described with four representative examples. Second, recent achievements in multiscale patterning are introduced with their strengths and weaknesses. Third, four application areas of wetting control, dry adhesives, selectively filtrating membranes, and multiscale tissue scaffolds are overviewed by stressing out how and why multiscale structures need to be incorporated to carry out their performances. Finally, we present future directions and challenges for scalable, multiscale patterned surfaces.

Strain-engineered manufacturing of freeform carbon nanotube microstructures

“…The ability to fabricate large arrays of 3D microstructures is also conducive to mimicry of nature's advanced functional materials 5 . We say this because the structures shown in Figs 2 and 5 have similar size and geometry to features on butterfly wings that have anisotropic wetting properties 45 , dry adhesive contacts on the legs of beetles and gecko lizards 3 , and microscale sensing hairs found on spiders 46 .…”

“…S calable fabrication of microstructures that mimic the hierarchical surface designs found in nature has been a long-standing aspiration of material scientists [1][2][3][4][5] . While symbiotic growth of the integrated circuit and microelectromechanical systems (MEMS) industries has enabled innovations in three-dimensional (3D) fabrication that leverage semiconductor processing tools, these methods, such as interference or inclined exposure lithography, are typically limited to arrays of identical structures [6][7][8] .…”

Hierarchical micro and nano structured, hydrophilic, superhydrophobic and superoleophobic surfaces incorporated in microfluidics, microarrays and lab on chip microsystems

“…Nevertheless, great progress has recently taken place for superoleophobic surfaces. Recent reviews on the topic include a detailed review by Liu et al on design, fabrication and application of superoleophobic surfaces [10], a shorter review from the same group by Xue et al focusing on superoleophobic polymers [11], one by Valipour et al stressing applications [12], another by Bellanger et al focusing on the physics and chemistry needed and on the theoretical background for such surfaces [13], yet another by Bae et al which emphasizes the role of hierarchy on bioinspired structures [14], and yet another by Chu and Seeger for superamphiphobic surfaces [15].…”

Enhanced resistance of nanocellular silica to dynamic indentation

“…They are widely applied for acoustic insulation, thermal management, catalytic reaction, drug delivery, energy storage, vibration damping, and impact and shock protection [3][4][5][6][7]. A few examples of cellular materials include woods [8,9], bones [10,11], carbon nanotube bundles [12], silica aerogels [13], expanded polymers [14,15], and cellular metals and ceramics [16][17][18][19].…”